Method of making multifocal lenses.



A. J. BOW-BBS. i METHOD OF MAKING MULTIFOGAL LENSES. APPLICATION FILEDJUNE 20, 1907.

t I A 11: I

\ inesfifis Q JMQM Patented Oct. 15, 1,912,

BI 12 115 [Tavern 07* i/eri JBowers. B M WW4 M 0 rney T ES; Parana onto.

ALBERT 'J. BownRS; or woncnsrsn, MASSACHUSETTS.

ME'rnon or MAKnve mnni irocar. LENSES.

mama's.

- which the following-is a specificationac- "toreceive a wafer oc'ompanied by drawings forming a part of thesame, in which-- I Figure 1represents a front view of a multifocal eyeglass embodying my invention,said eyeglass containing lens having three focal powers. Fig.2represents in sectional view a piece of glass known as'crown glass, andillustrating the first step in my 1mproved method of constructing amultifocal lens. Fig. 3 represents the same piece with on .of itssurfaces ound in concave form Fflint glass, whereby the second focalpower of the lens is produced, and illustrating the second step in myimprovedmethod. Fi 4. represents a piece of flint glass fromfwh ch oneof the'wafers is formed. Fig. 5'represents the same piece of. glassground on one sideto produce a convex surface fitting the concavesurface of the lens, and illustrating the third step in my improvedmethod. Fig. 6 represents the piece shown in Fig. 5 as applied to thepiece re resented in Fig. 3 and united thereto by proved method ofconstruction. Fig. 7 illustrates the fifth step which consists. ingrindof the lens and united therewith by fusion,

and illustratin the seventh step in my impreved metho Fig. 11illustrates the eighth step in my improved method which consists informing a convex surface upon one side of the lens of the requiredcurvature to form the lens. Fig. 12 illustrates the ninth step whichconsists in grinding the opposite side of the lens to form a concavesur- Speciflcation of Letters Patent.

sion of their contacting surfaces, and illustrating the fourth step 1nmy 1mratemea @ct. is, rare.

Application filed-June 20, 1901 'Serial No. 379,990.

face to complete the lens, having the required refraction in the crownglass Section to give the third focal power between the lines a, oi thesecond focal power between the lines a a and the first focal power hetweenthe lines a", a and Fig. 13 represents the same view as Fig. 6,Showing a single piece of flint glass applied to the crown glass whichhas been ground to complete a lens conforming in cross section to thespace inclosed between the broken lines 6, 6 thereby completing a lenshaving two focal powers only and embodying a single wafer of flintglass.

Similar reference letters and fi res refer to similar parts in thedifferent views.

My invention relates to that class of lenses which are composed ofsuperimposed layers of glass having different refractive powers, thesurfaces of said layers being curved, whereby the refraction of theindividual layers is determined, and it has for its objects tofacilitate the grinding of the com- 'posite lens, to secure greateraccuracy in the ground surfaces, to better enable the composite parts ofthe lens to be united by fusing their contacting surfaces withoutinjury, and

-to avoid ahyerrors in the construction of the lens due to slightdisplacement of the wafers,- and I accomplish these objects by theprocess of manufacture as hereinafter described and pointed out in theannexed claims.

My invention is carried into eflect as follows :I first prepare a pieceof glass, preferably of the refractive power known as crown glass, ofany suitable size or shape in plan view to form the desired eye of theeyeglass or spectacle, but having its cross section in the plane of theminor axis of the finished lens in the form of a truncated triangle, asshown at A,'Fig. 2, with one side 1 at right angles with the oppositeends 2, 3, and with the other side 4 lying in a plane at an obliqueangle to the side 1. The oblique side 4 is then ground to form a concavecircular'recess 5, the curvature of the concave surface 6, forming thebottom of the recess,

being determined by the required focal power of a wafer, preferably madeof, flint glass or glass having a different refractive power from thatof crown glass of which the piece A is composed. The concaving of theoblique surface 4 extends entirely across the piece A with the axis ofits curvature lying in a plane at right angles to the oblique side 4. Apiece of flint glass B, of suflicient size to form one of the waferspreferably circular in plan view, is then ground upon one side to form aconvex surface 7 having a curvature equal to that of the curved surface6, Fig. 3. The piece B having .been thus ground on one side is appliedto the piece A, and near one'edge thereof as shown in Fig. 6. Thecontacting curved surfaces are then united, preferably bg fusion, andthe combined pieces A and after having been attached, as shown in Fig.6, are again ground to form a concave surface 8 having the pro ercurvature to secure, when the second v We er of flint glass is applied,the third desired focal power. A second piece of flint glass C, as shownin Fig. 8, is then ground on one side to produce a convex surface 9, asshown in Fig. 9, corresponding to the curvature of the concave surface8. The .piece C is then applied to the piece A, somewhat nearer itscenter then the piece B and,

if necessary, overlapping the piece B. The

contacting surfaces are then united, preferably by'fusion, and thecomposite surface is again ground in convex form having a curvature as:shown at 10, Fig. 11, and the eyeglass is then completed by grinding acorresponding concave surface on the opposite side, as shown at 11',Fig. 12. When thus completed the eyeglass will possess three focalpowers, one between the points .a, a determined by the refractive powerof the crown glass and the curvature of the lens; a second focal powerbetween the points a, 0 due to the combined but different refractivepowers of the crown glass and flint glass and the shape in cross sectionof the flint glass as determined by the curved 40 surface 10, whichforms the outer surface of the lens, and the curved surface 8, whichforms the seat of the flint glass wafer C,

and a third focal power between the points a a due to the combinedrefractive power of the fl-int glass wafer B and the shape in crosssection of the flint glass as determined by the-curved surface 10and'the curved surface 6, which forms the seat of the flint glass waferB. The eyeglass shown in Fig. 12'possesses, therefore, three focalpowerswhich may be adapted for distant, medium, and near to vision; butin case two 'focal powers only are required the combined pieces'A and Bafter having been attached, as shown in Fig. 6 and again in Fig. 13, areground to form a concavo-convex lens by grmdingthe com.- bined p'eces Aand B on the broken curved lines 12 and 13, Fig. 13.

- I am aware that it is not new to form an eyeglass having more than onefocal power by the combinationof two pieces of glass having differentrefractive powers, such as crown glass and flint glass, and I am awarealso that such pieces have had their contact- -center or axis ofthelens, for example, the

ing surfaces united by fusion. In the construction ofan eyeglass of thiskllld, however, it has. been the practice to form a concave recess inthe surface of a piece of crown powers.

'By my improved method I form-the concave recess for the first waferupon one side of' a piece of crown glass A which is considerably thickerat one edge than the other, which enables. me to grind the concaverecess, covering substantially the entire area of the-eyeglass, the arcof this curvature extending across the glass from its thin to its thickedge, thereby securing the following advantages among others in theprocess ofmanufacture; greater accuracy is secured in the curvature ofthe surface which is to form the seat than when a small recess only isformed; the wafer is supported throughout its entire extent upon itscurved seat; it becomes unnecessary to accurately determinethe ositionof the curved seat, as in the case 0 a small recess,"for the entire surface of the eyeglass possesses the required curvature and the wafer canbe attached in any position desired; in grinding the eye glass thegrinding operation takes place,- simultaneously uponopposite sides ofthe first ground surface to form theconcave surface 6 extends entirelyacross the piece of crown. glass and ingrinding the second curved seatformed by the surface '8 the grinding takes place on opposite sides ofthe center of the lens, namely, upon the flint glass wafer B andupon theedge14 of the crown glass, likewise in grinding the convex surface 10the grinding takes place on opposite sides of the, center, namely, uponthe flint wafer C and upon the edge 15 of the crown glass. By making thecurved seats for the flint glass wafers to extend substantiallyacross'115 the entire width of the crown lass I am able to apply piecesB and O o considerably larger slze than the size of the finished wafersand support them throughout their entlre area, w I

which also enablesme to place the first wafor B at the extreme edge ofthe crown glass, and to leave a comparatively thick edge, as shown at16, Figs. 7 and 10, after the curved surface 8 is formed. Y V

In practice, I prefer to perform the several steps in the operation ofmaking a multifocal lens in the order named above; but the same resultmay be secured by forming ich facilitates the process-of 1 20 vfuslngthe contactmg surfaces together-and the concave surface 11 in the pieceA, by

pressing or otherwise, before the curved seat 6 is formed for the firstwafer. When this is done the entire piece A as shown in Fig.

2, is pressed into the form or molded with its under side concaved asshown in Figs. 12 and 13,. only requiring to be polished and avoidingthe necessity of grinding-away so much material. By my improved methodof constructing lenses having three focal powers, I am enabled to placethe wafer,

giving the intermediate focal distance outside and overlapping the wafergiving the shortest focal distance, and as the focal power of bothwafers is determined by the curvature of the seat, I am able to grindthe edges of both wafers extremely thin, and I am also able to unite theseveral pieces of: flint glass by fusion inasmuchas the pieces are ofsubstantially uniform thickness in cross section, and they are bothfusedbefor'e their edges have beencredu ced in thickness,=]

causing the heat to be equally diffused throughout the entire mass ofglass.

I claim,

1. The method of making a multifocal lens from a piece of glass ofsuitable size'to form the completed lens by attaching a wafer to itssurface in the following manner; by grinding one side of said piece in acurve determined bythe desired curvature of the contacting surface ofthe wafer, with said curve extending entirely across said side andlarger in area than said completed wafer, attaching in any desiredposition on' said curved surface a segment, of area smaller than. saidcurved surface and designed to form said Wafer, then grinding said piecewith said segment attached to form the com-,

pleted lens. I

2. The method of making a multifocal lens from a piece of glass ofsuitable size to form the completed lens, having its cross section inthe plane of the minor axis of the finished lens with one oblique side,byattaching a wafer to said obllque side in the following manner; bygrinding said entire oblique side in a curve determined by the desiredcurvature of the contacting surface of the wafer, said curvature of larer area 7 than said completed wafer, attac ling in any desired positionon said curved surface a segment, of area smaller than said curvedsurface and designed to form said wafer, then grindingthe said piecewith said segment attached to form the completed lens.

3. 'The method of making a multifocal lens from a piece of glass ofsuitable size to form the, desired lens by attaching two or more wafersto its surface in the following manner, first, grinding one side of saidpiece of glass in the desired curve of the contacting face of the firstWafer, said curve extending entirely across said side, permanentlyattaching to a portion of said curved surface a segment deslgned to formthefirst wafer, then grinding said entire curved surface and the segmentattached theretoin the desired curve, of the contacting face of thesecond wafer, permanently attaching to a portion of the said secondcurved surface a segment designed to form the second wafer,

with part of its surface in contact with said and of suita le size toform the desiredlens by permanent-1y attachin successive seg- 'mentsdesigned to form t e wafers to suc- "cessive curved seats'in the obliqueside of segment in a different position on its seat with relationto thecenter of the lens, and grinding the united piece of glass and segmentsto form the completed lens.

' J ALBERT J. BOWERS. Witnesses: PENELOPE CoMBERBAcH, Burns B. FOWLER.

